fix(website): align the language picker chevron (#3805)

* fix(website): align the language picker chevron

Replace the font-dependent down glyph with a fixed-size SVG mask that
inherits the button color and aligns within its existing flex layout.
Rotate the chevron when the native details menu is open.

Refs #3804

* fix(website): preserve the chevron in forced colors

website/public/assets/styles.css

@@ -184,8 +184,23 @@ section[id] {
   display: none;
 }
 .language-picker summary::after {
-  content: "⌄";
+  content: "";
   flex-shrink: 0;
+  inline-size: 0.75rem;
+  block-size: 0.75rem;
+  background-color: currentColor;
+  mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 12 12'%3E%3Cpath d='m2 4 4 4 4-4' fill='none' stroke='black' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E")
+    center / contain no-repeat;
+}
+.language-picker[open] summary::after {
+  transform: rotate(180deg);
+}
+@media (forced-colors: active) {
+  .language-picker summary::after {
+    /* Keep the mask visible with the user's high-contrast text color. */
+    forced-color-adjust: none;
+    background-color: CanvasText;
+  }
 }
 .language-picker nav {
   position: absolute;